Repair or replace: how to decide

A roofer called out for a leak or worn shingles will usually recommend either a repair or a new roof, and most give that advice honestly. It still helps to know how the decision is usually made before anyone quotes. The five questions below are best taken in order.

1. How old is the roof?

Asphalt shingles wear out. Older three-tab shingles often last around 20 years, and heavier architectural shingles often 20 to 30. Strong sun, poor attic ventilation and frequent storms shorten both. Metal, tile and slate usually last far longer, so on those roofs the answer is more often a repair.

If you do not know the age, purchase paperwork or a permit record may say. The shingles give clues too: curling edges, bare patches where granules have worn away, and heavy granule buildup in the gutters all suggest a roof in its later years. A roof in the first half of its life with a single problem is usually a candidate for repair. Near the end of its expected life, the other questions carry more weight.

2. How much of the roof is affected?

Damage confined to one area is usually repairable: a few shingles lifted by wind, one cracked pipe boot, one poorly flashed chimney. As a rough guide, once problems cover more than a quarter to a third of the roof, replacement starts to make more sense. Every repair visit carries its own setup and access costs, and widespread wear tends to bring the next repair soon after the first.

3. Is the problem the shingles or the joins?

Many leaks on otherwise sound roofs come from flashing rather than shingles. Pipe boots, chimney flashing and missing kickouts can usually be fixed without touching the rest of the roof. What flashing is, and why leaks often start there covers where to look.

If a contractor recommends a full replacement to solve a single leak, ask where they think the water is getting in. If the answer is a flashing point, ask what a repair would involve.

4. How many layers are already on?

Some roofs have had new shingles laid over the old ones. That costs less at the time, but it adds weight and hides the decking. Codes generally do not allow another overlay where two layers already exist, so a roof with two layers will need a full tear-off, which adds to the cost.

The number of layers can sometimes be seen at the roof edge, but checking is a job for a roofer or an inspector. Do not climb up to look.

5. What condition is the decking in?

Under the shingles is the decking, usually plywood or oriented strand board. Long-term leaks soften it. From the ground you may see a dip between rafters. From the attic, if you can reach it safely through a proper hatch, you may see dark stains or daylight. Once up there, step only on joists or boards, never on the ceiling between them.

Soft decking cannot be covered over. It has to be cut out and replaced, and that work is usually priced per sheet on top of the roof itself. Widespread soft decking generally points toward replacement.

Cases that sit on the line

• You plan to sell soon. Buyers and their inspectors look closely at older roofs. A replacement may not pay for itself in the sale price, while a documented repair may be enough. A local real estate agent can tell you what buyers in your area tend to expect.
• The damage came from a storm. If insurance may cover part of the cost, stay off the roof, photograph the damage from the ground, report it under your policy's terms, and check with your insurer before permanent repairs.
• Repair shingles will not match. Older shingles fade and styles are discontinued. A mismatched patch is cosmetic, but it matters more to some owners than to others.
• You have paid for several repairs in a few years. At that point a harder look at the whole roof is sensible.

A simple way to weigh it

If the answers are mixed, compare what each path costs per year.

1. Add the repair quote to a realistic estimate for the next repair, then divide that total by the number of years the repairs will realistically buy.
2. Divide the replacement quote by the expected life of a new roof.
3. Compare the two yearly figures.

Say a repair costs $900 and the next repair is likely to cost about $1,100, for $2,000 in total. If those repairs keep the roof sound for four more years, they cost $500 a year. A replacement quoted at $15,000, with shingles expected to last 25 years, costs $600 a year. Here the repair is cheaper per year. If the same $2,000 bought only one good year, it would cost $2,000 a year, and replacement would be the better value.

Who can help answer these questions

A roofer can assess the layers, the decking and the flashing, and a home inspector can describe the roof's condition as part of a wider inspection. A second opinion is reasonable for a large decision. Before you hire either, read the hiring checklist. Insurance and pre-purchase roof inspection reports explains what a condition report can and cannot tell you.